This invention relates in general to polymers, and in particular to an ionically conductive polymer for use in fuel cells and other electrochemical devices. For example, the polymer may be used for producing fuel cell membranes and/or as a binder in fuel cell electrodes.
A fuel cell is an electrochemical device that continuously converts chemical energy into electric energy and some heat for as long as fuel and oxidant are supplied. Fuel cells are evolving. Some currently known categories of fuel cells include polymer electrolyte membrane (PEM), alkaline, phosphoric acid, molten carbonate, solid oxide, and microbial/enzyme based.
At the heart of the PEM fuel cell is a membrane electrode assembly (MEA). The MEA includes a membrane made from a polymer electrolyte or proton conducting polymer. The polymer electrolyte membrane is sandwiched between a pair of electrodes called an anode and a cathode. The MEA also usually includes porous, electrically conductive sheets called gas diffusion layers positioned adjacent to the electrodes to permit diffusion of reactants to the electrodes.
In operation, a fuel such as hydrogen or methanol is flowed into contact with the anode where it dissociates into electrons and protons. The electrons, which cannot pass through the polymer electrolyte membrane, flow from the anode to the cathode through an external circuit containing an electric load, which consumes the power generated by the fuel cell. The protons pass through the polymer electrolyte membrane and combine with oxygen and electrons on the cathode to produce water and heat.
Typically polymer electrolytes require a sufficient level of hydration in order to effectively conduct protons through the membrane. However, fuel cells are sometimes operated under conditions in which the polymer electrolyte membrane has a low water content, for example, under conditions of low relative humidity (RH) and/or high temperature. Various approaches have been used to increase the proton conductivity of polymer electrolyte membranes under these conditions but none have been totally successful.